In recent years a large amount of research has been conducted in the development of fiber-reinforced composites for aerospace applications. An air-frame fabricated from a composite or any other material requires a large number of fasteners. Since there is a tendency for cracks to develop at fastener holes, the area in the vicinity of a fastener is of importance from a structural integrity standpoint. The detection of cracks is difficult and in many cases impossible because of component overlap. Accordingly, the prevention of cracks in the first place becomes of vital importance. To this end, some degree of plasticity of the importance. To this end, some degree of plasticity of the material in the vicinity of the fastener hole is a desirable attribute. To be able to take advantage of fiber-reinforced composite materials in air-frame construction, a reinforcing fiber or filament is required that is capable of plastically deforming around the holes so as to minimize the possibility of crack initiation. Graphite and boron fibers, conventionally used as reinforcing agents, do not possess the requisite combination of strength and plasticity.
In engine manufacture the technology is available for fabricating gas turbine compressor blades from graphite and boron fiber-reinforced epoxy resin composites. However, blades made from these materials are incapable of satisfactorily withstanding the impact of foreign objects ingested by the engine. As discussed above, the deficiency is attributable to the lack of important properties in the presently available reinforcing fibers.
In the aerospace industry there is a growing interest in the development of powder metallurgical processes. The present high cost of titanium alloy structural components stems from the large volume of material input in the form of forgings and extrusions for structural components and the associated expense of machining away excess material. Powder metallurgy is a technology that offers a solution to these problems. While significant strides are being made in the area of manufacturing techniques for making shapes from powder, there is a problem in developing a suitable powder that can be compacted, e.g., by vacuum hot pressing or hot isostatic pressing, to provide shapes having superior mechanical properties.
It is a principal object of this invention, therefore, to provide a high specific strength polycrystalline titanium-based alloy which can be in the form of a filament suitable for use in reinforcing composites or in the form of a powder suitable for use in fabricating structures by powder metallurgical processes.